Re: [RFC] fix VMX TSC synchronicity

[Andi Kleen <andi-Vw/NltI1exuRpAAqCnN02g@public.gmane.org>]

On Wed, Jan 16, 2008 at 10:46:11AM +0200, Avi Kivity wrote:
> [fixing gmane emails, urgfhsz]
> 
> Andi Kleen wrote:
> >Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org> writes:
> >
> >  
> >>Thanks; that's reassuring to know that it will work (at least on Intel).
> >>    
> >
> >Actually there are modern Intel systems which still have instable TSCs;
> >e.g. IBM Summit multi node systems and some others. So you should
> >still handle that case.
> >  
> 
> I really don't see any way we could.  If the guest assumes tscs are 
> synchronous, and they really are not, there's nothing we can do.

Linux checks a couple of things: e.g. if there are no deep C states
and if there are no clustered nodes in the APIC etc.

It might be reasonable to check the clock source of the kernel
and if it's not TSC force one of these in the emulated firmware
environment

> You might taskset guests into a single node on such systems, which is a
> good idea anyway.

Ah pushing the problem to the user. An easy, but typically wrong, solution.

-Andi

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